The invention relates to polymerizing radiopaque compositions that include cationically active functional groups and radiopacifying fillers.
Fillers are often added to polymer resins to form composites having higher strength values than the polymer resin itself. Dental composites, for example, typically feature high filler loadings on the order of 50% by weight or higher.
Non-radiopacifying fillers such as quartz and silica have been successfully combined with free radically polymerizable components such as acrylates and methacrylates and a free radical initiator to form a useful dental composite following exposure to polymerization conditions. Such fillers also have been successfully used with cationically polymerizable components such as epoxy resins and a cationic initiator to form useful dental composites following cationic-initiated polymerization.
In many instances it is desirable to use a radiopacifying filler to create a radiopaque composite. Such composites are particularly useful in dental applications because the composite is x-ray detectable. Radiopacifying fillers have been successfully combined with free radically polymerizable components and free radical initiators to form dental composites. It would also be desirable to combine radiopacifying fillers with cationic initiators and cationically polymerizable components such as epoxy resins which undergo less shrinkage than acrylates and methacrylates upon polymerization.
Although there is a need for a radiopaque composite prepared by combining a cationic initiator, a cationically polymerizable component and a radiopacifying filler, the inventors have discovered that, unlike free radically polymerizable systems, not all polymerizable resin-filler-initiator combinations will produce a useful composite (i.e., a radiopaque composite having a Barcol hardness of at least 10 measured using a GYZJ-935 meter) upon exposure to polymerization conditions. In many cases, the inventors have discovered, the radiopacifying filler inhibits or suppresses the cationic polymerization mechanism. In some cases, the net result is a composite having a hardness value lower than the hardness value of the unfilled resin.
The inventors have now discovered that certain radiopacifying fillers, when combined with cationic initiators and cationically polymerizable components, will produce composites having a Barcol hardness of at least 10 (measured using the GYZJ-935 meter) following exposure to polymerization conditions. In some cases, this requires treating fillers that would otherwise interfere with the cationic polymerization mechanism, e.g., by heating or coating the fillers. The inventors have further identified selection criteria that can be used to screen cationic initiator-resin-radiopacifying filler combinations. The inventors have thus made it possible to prepare useful composites based upon cationic initiators, cationically polymerizable resins, and radiopacifying fillers.
Accordingly, the invention features, in a first aspect, a polymerizable composition that includes:
(a) a cationically active functional group;
(b) an initiation system capable of initiating cationic polymerization of the cationically active functional group; and
(c) a filler composition comprising a radiopacifying filler in an amount sufficient to render the polymerizable composition radiopaque. The radiopacifying filler is selected from the group consisting of metal oxides, metal halides, metal borates, metal phosphates, metal silicates, metal carbonates, metal germanates, metal tetrafluoroborates, metal hexafluorophosphates, and combinations thereof. The combinations may be in the form of physical blends or chemical compounds.
Components (a), (b), and (c) are selected such that the polymerizable composition polymerizes to form a polymerized composition having a Barcol hardness, measured according to Test Procedure A, infra, using a GYZJ-935 meter, of at least 10 within 30 minutes following initiation of the cationically active functional group at a reaction temperature of 25 C. Initiation can be determined using differential scanning calorimetry, and is manifested as an increase in enthalpy.
As used herein, a xe2x80x9cradiopaque compositionxe2x80x9d is a composition that has the ability to diminish the path of x-rays to the same extent as an aluminum sample having the same thickness such that the density of an x-ray image of the composition is less than the density of the x-ray image of the aluminum, determined according to Procedure 7.11 of International Standard IS04049; 1988(E), xe2x80x9cDentistryxe2x80x94Resin-Based Filling Materials.xe2x80x9d
A xe2x80x9ccationically active functional groupxe2x80x9d is a chemical moiety that is activated in the presence of an initiator capable of initiating cationic polymerization such that it is available for reaction with other compounds bearing cationically active functional groups.
A xe2x80x9cfree radically active functional groupxe2x80x9d is a chemical moiety that is activated in the presence of an initiator capable of initiating free radical polymerization such that it is available for reaction with other compounds bearing free radically active functional groups.
A xe2x80x9cmetal oxidexe2x80x9d is a compound that contains only a metal and oxygen.
A xe2x80x9cmetal halidexe2x80x9d is a compound that contains, at a minimum, a metal and a halogen (e.g., chlorine, bromine, iodine, or fluorine).
A xe2x80x9cmetal boratexe2x80x9d is a compound that contains, at a minimum, a metal, boron, and oxygen.
A xe2x80x9cmetal phosphatexe2x80x9d is a compound that contains, at a minimum, a metal, phosphorous, and oxygen.
A xe2x80x9cmetal silicatexe2x80x9d is a compound that contains, at a minimum, a metal, silicon, and oxygen. Thus, for example, a metal aluminosilicate containing a metal, aluminum, silicon, and oxygen would be considered a xe2x80x9cmetal silicatexe2x80x9d for the purposes of this invention.
A xe2x80x9cmetal carbonatexe2x80x9d is a compound that contains, at a minimum, a metal and a CO3 group.
A xe2x80x9cmetal germanatexe2x80x9d is a compound that contains, at a minimum, a metal, germanium, and oxygen.
A xe2x80x9cmetal tetrafluoroboratexe2x80x9d is a compound that contains only a metal and a BF4 group.
A xe2x80x9cmetal hexafluorophosphatexe2x80x9d is a compound that contains only a metal and a PF6 group.
The composition may also include a free radically polymerizable component such as an acrylic or methacrylic acid ester. Such compositions are often referred to as xe2x80x9chybridxe2x80x9d compositions. In a hybrid composition, free radical polymerization of the free radically active functional groups assists in obtaining the requisite Barcol hardness value of the composite. Nevertheless, even in hybrid compositions it is cationic polymerization of the cationically active functional group that preferably forms a polymerized composition having the requisite hardness value under the polymerization conditions described above.
In some embodiments, the polymerizable composition polymerizes to form a polymerized composition have a Barcol hardness, measured using a GYZJ-934-1 meter according to Test Procedure A, infra, of at least 10 within 30 minutes following initiation of the cationically active group.
The inventors have identified several screening tests for use in designing successful polymerizable compositions. Preferably, these tests are used in combination with each other.
One test focuses on the radiopacifying fillers themselves and is based upon isoelectric point measurements. The isoelectric point of any particular radiopacifying filler is independent of filler loading. However, the filler loading influences which values of isoelectric point are required in order to result in a successful cationic polymerization. According to this test, therefore, the filler composition is selected such that when the amount of the radiopacifying filler is at least 50% by weight of the polymerizable composition, the radiopacifying filler has an isoelectric point, measured according to Test Procedure B, infra, of no greater than 7.
Other tests focus on the interaction between the radiopacifying filler and a test polymerizable composition that includes a cationically polymerizable component and a cationic initiator. According to one such test, the filler composition is selected such that when the amount of the filler composition is 70% by weight of the polymerizable composition, a test polymerizable composition defined in Test Procedure C, infra, that includes the filler composition has an adsorption value of no greater than 20 micromoles/g filler, as determined by surface area titration according to Test Procedure C. When the amount of the filler composition is 50% by weight of the polymerizable composition, the adsorption value is no greater than 80 micromoles/g filler.
According to another test, the filler composition is selected such that when the amount of the filler composition is 70% by weight of the polymerizable composition, the filler composition causes a change in conductivity of a test solution of no greater than 60 mV, determined according to Test Procedure D, infra. When the amount of the filler composition is 50% by weight of the polymerizable composition, the change in conductivity is no greater than 125 mV.
The selection criteria are phrased in terms of certain filler loadings. However, it should be understood that the particular filler loading is provided as a test. Accordingly, polymerizable compositions having filler loadings different from the loadings associated with the selection criteria are within the scope of the invention provided that, for any particular filler/resin/initiator combination, if the filler loading were the same as the amount recited in the selection criteria, the requirements of those criteria would be met.
Both the chemical composition and physical form of the radiopacifying filler, including its surface characteristics, as well as the process used to prepared the filler, are variables which influence the effect of the filler on the cationic polymerization mechanism for a given polymerizable resin-filler-initiator combination. Sol-gel-derived, melt-derived, vapor-derived, and mineral radiopacifying fillers can be used. The radiopacifying filler may also be in the form of one or more inorganic radiopacifying particles dispersed in a polymer matrix. In the case of sol-gel-derived fillers, the filler composition is selected such that the filler composition has a relative peak height of greater than 80% as determined by Fourier transform infrared spectroscopy according to Test Procedure E, infra.
Semi-crystalline and amorphous microstructures are generally preferred. An xe2x80x9camorphousxe2x80x9d filler is one which does not give rise to a discernible x-ray powder diffraction pattern. A xe2x80x9csemi-crystallinexe2x80x9d filler is one which gives rise to a discernible x-ray powder diffraction pattern.
With respect to chemical composition, the radiopacifying filler preferably includes an element having an atomic number of at least 30. Examples include yttrium, strontium, barium, zirconium, hafilium, niobium, tantalum, tungsten, molybdenum, tin, zinc, lanthanide elements (i.e., elements having atomic numbers ranging from 57 to 71, inclusive), and combinations thereof. Particularly preferred are radiopacifying fillers that include: (a) an oxide selected from the group consisting of lanthanum oxide, zinc oxide, tantalum oxide, tin oxide, zirconium oxide, yttrium oxide, ytterbium oxide, barium oxide, strontium oxide, and combinations thereof, combined with (b) an oxide selected from the group consisting of aluminum oxide, boron oxide, silicon oxide, and combinations thereof. Specific examples of suitable radiopacifying fillers include the following:
(a) Fillers that include 0.5% to 55% by weight lanthanum oxide and 45% to 99% by weight silicon oxide. The fillers preferably have a semi-crystalline or amorphous microstructure. In terms of processing, the fillers are preferably sol-gel- or melt-derived.
(b) Fillers that include 0.5% to 55% by weight lanthanum oxide, 0.5% to 50% by weight aluminum oxide, and 0.5% to 90% by weight silicon oxide. The fillers preferably have a semi-crystalline or amorphous microstructure. In terms of processing, the fillers ar preferably sol-gel- or melt-derived.
(c) Fillers that include 0.5% to 55% by weight lanthanum oxide, 0.1% to 55% by weight aluminum oxide, 0.01% to 80% by weight boron oxide, and 1% to 90% by weight silicon oxide. The fillers preferably have an amorphous microstructure. In terms of processing, the fillers are preferably sol-gel- or melt-derived.
(d) Fillers that include 0.5% to 55% by weight lanthanum oxide, 0.01% to 80% by weight boron oxide, and 1% to 90% by weight silicon oxide. The fillers preferably have a semi-crystalline or amorphous microstructure. In terms of processing, the fillers are preferably sol-gel- or melt-derived.
(e) Fillers that include 0.5% to 55% by weight zinc oxide, 0.5% to 55% by weight lanthanum oxide, 0.1% to 40% by weight aluminum oxide, 0.01% to 80% by weight boron oxide, and 1% to 80% by weight silicon oxide. The fillers preferably have an amorphous microstructure. In terms of processing, the fillers are preferably melt-derived.
(f) Fillers that include colloidally derived zirconium oxide.
(g) Fillers that include 0.5% to 55% by weight zirconium oxide and 45% to 99% by weight silicon oxide. The fillers preferably have a semi-crystalline or amorphous microstructure. In terms of processing, the fillers are preferably sol-gel-derived.
(h) Fillers that include 0.5% to 55% by weight zirconium oxide, 0.01% to 40% by weight boron oxide, and 1% to 90% by weight silicon oxide. The fillers preferably have a semi-crystalline or amorphous microstructure. In terms of processing, the fillers are preferably sol-gel-derived.
(i) Fillers that include 0.5% to 55% by weight yttrium oxide and 1% to 90% by weight silicon oxide. The fillers preferably have a semi-crystalline or amorphous microstructure. In terms of processing, the fillers are preferably derived from a sol-gel. The fillers preferably have a semi-crystalline or amorphous microstructure. In terms of processing, the fillers are preferably sol-gel-derived.
(j) Fillers that include 0.5% to 55% by weight yttrium oxide, 0.1% to 50% by weight aluminum oxide, and 1% to 90% by weight silicon oxide. The fillers preferably have a semi-crystalline or amorphous microstructure. In terms of processing, the fillers are preferably sol-gel- or melt-derived.
(k) Fillers that include 0.5% to 55% by weight barium oxide, 0.1% to 40% by weight aluminum oxide, 0.01% to 80% by weight boron oxide, and 1% to 90% silicon oxide. The filler preferably has an amorphous microstructure. In terms of processing, the fillers are preferably is melt-derived.
(l) Fillers that include 0.5% to 55% by weight strontium oxide, 0.1% to 40% by weight aluminum oxide, 0.01% to 80% by weight boron oxide, and 1% to 90% by weight silicon oxide. The filler preferably has an amorphous microstructure. In terms of processing, the fillers are preferably derived from a melt.
(m) Fillers that include a fluoride such as a lanthanide fluoride (e.g., ytterbium fluoride), yttrium fluoride, zinc fluoride, tin fluoride, and combinations thereof.
In some cases, the above-described radiopacifying fillers may be used xe2x80x9cas is.xe2x80x9d In other cases, it is necessary to treat the fillers, e.g., by heat treating the fillers or by coating them. Accordingly, even fillers which do not meet the above-described selection criteria initially can be used successfully if treated properly.
The coated radiopacifying fillers include a core having a first chemical composition and a coating (which may or may not be continuous) on the surface of the core having a second chemical composition different from the first chemical composition. Examples of useful core materials include quartz, fused quartz, silicate glass (including borosilicate glass), zirconium oxide-silicon oxide, zirconium oxide-boron oxide-silicon oxide, and combinations thereof. Examples of useful coatings include silicate glass (including borosilicate glass), boron oxide, colloidally derived silicon oxide, colloidally derived zirconium oxide, and combinations thereof. Polymer coatings can also be used. In some cases, the coating offers the additional advantages of reducing shrinkage upon polymerization and opacity. The reduced opacity, in turn, enhances the ability to obtain good depth of cure in photopolymerizable compositions. The coating may also provide anchorage for, e.g., silane treatments.
The amount of filler composition preferably is at least 50% by weight, and more preferably at least 70% by weight, based upon the total weight of the polymerizable composition. In addition to the radiopacifying filler, the filler may include non-radiopacifying fillers such as quartz, calcium carbonate, feldspar, KBF4, cryolite, and combinations thereof.
The initiator system is preferably a photoinitiator system. Photoinitiated compositions preferably polymerize to form a polymerized composition having a depth of cure of at least 2 mm, preferably at least 6 mm, and more preferably at least 8 mm within 30 minutes following initiation of the cationically active functional group at a reaction temperature of 37xc2x0 C. Useful initiator systems include onium salts such as iodonium and sulfonium salts, and organometallic complex salts.
Examples of suitable materials having cationically active functional groups include epoxy resins, vinyl ethers, spiro ortho esters, spiro ortho carbonates, bicylic ortho esters, bicyclic monolactones, bicyclic bislactones, cyclic carbonates, and combinations thereof. Such materials can be used alone or combined with reactants having free radically active functional groups to form hybrid compositions. It is also possible to include reactants that contain both free radically active functional groups and cationically active functional groups in a single molecule.
In the case of hybrid compositions, the composition may include a separate initiator system capable of initiating free radical polymerization of the free radically active functional group. Alternatively, the composition may include a single initiator system capable of initiating both free radical and cationic polymerization.
Examples of useful polymerizable compositions include dental composites, orthodontic bracket adhesives, and orthodontic band cements. As used herein, the term xe2x80x9ccompositexe2x80x9d refers to a filled dental material. The term xe2x80x9crestorativexe2x80x9d refers to a composite which is polymerized after it is disposed adjacent to a tooth. The term xe2x80x9cprosthesisxe2x80x9d refers to a composite which is polymerized for its final use (e.g., as crown, bridge, veneer, inlay, onlay or the like) before it is disposed adjacent to a tooth. The term xe2x80x9csealantxe2x80x9d refers to a lightly filled composite which is polymerized after it is disposed adjacent to a tooth. Each of these materials is suitable for temporary or permanent use.
In a second aspect, the invention features a photopolymerizable dental composite that includes:
(a) a cationically active functional group;
(b) a photoinitiation system capable of initiating cationic polymerization of the cationically active functional group upon exposure to visible light; and
(c) a filler composition comprising a radiopacifying filler in an amount sufficient to render the polymerizable composition radiopaque. Upon exposure to visible light, the composite polymerizes to form a polymerized dental composite having a Barcol hardness, measured according to Test Procedure A, infra using a GYZJ-935 meter, of at least 10 within 30 minutes following initiation of the cationically active functional group at a reaction temperature of 25xc2x0 C. The composite may further include an ethylenically unsaturated reactant, as described above.
Preferably, the resulting composite has a Barcol hardness, measured using a GYZJ-934-1 meter according to Test Procedure A, of at least 10 within 30 minutes following initiation of the cationically active functional group at a reaction temperature of 25xc2x0 C. The amount of filler in the composite preferably is at least 50% by weight based upon the total weight of the polymerizable composite. The composite preferably polymerizes to form a polymerized composite having a depth of cure of at least 2 mm within 30 minutes following initiation of the cationically active functional group at a reaction temperature of 37xc2x0 C.
In a third aspect, the invention features a polymerizable composition that includes:
(a) a cationically active functional group;
(b) an initiation system capable of initiating cationic polymerization of the cationically active functional group; and
(c) a filler composition comprising a radiopacifying filler other than a sulfate in an amount sufficient to render the polymerizable composition radiopaque. Components (a), (b), and (c) are selected such that the polymerizable composition polymerizes to form a polymerized composition having a Barcol hardness, measured according to Test Procedure A, infra, using a GYZJ-935 meter, of at least 10 within 30 minutes following initiation of the cationically active functional group at a reaction temperature of 25xc2x0 C.
In a fourth aspect, the invention features a method of preparing a polymerized composition that includes:
(a) providing a polymerizable composition that includes (i) a cationically active functional group; (ii) an initiation system capable of initiating cationic polymerization of the cationically active functional group; and (iii) a filler composition that includes a radiopacifying filler in an amount sufficient to render the composition radiopaque; and
(b) initiating polymerization of said cationically active functional group to form said polymerized composition, preferably at a reaction temperature of 37xc2x0 C. or less. The radiopacifying filler is selected from the group consisting of metal oxides, metal halides, metal borates, metal phosphates, metal silicates, metal carbonates, metal germanates, metal tetrafluoroborates, metal hexafluorophosphates, and combinations thereof, where these terms have the meanings set forth above. The polymerizable composition is selected such that it is capable of polymerizing to form a polymerized composition having a Barcol hardness, measured according to Test Procedure A, infra, using a GYZJ-935 meter, of at least 10 within 30 minutes following initiation of the cationically active functional group at a reaction temperature of 25xc2x0 C. Examples of useful polymerized products include dental composites.
In one embodiment, the initiation system is a photoinitiation system, in which case the method includes exposing the polymerizable composition to actinic radiation to initiate polymerization of the cationically active functional group. Preferably, the initiation system includes a visible light sensitizer as well such that polymerization is initiated by exposing the composition to visible light. Other suitable sources of actinic radiation include sources of ultraviolet radiation. Thermal initiation systems may also be used, in which case the method includes exposing the composition to thermal radiation to initiate polymerization of the cationically active functional group.
The inventors have further discovered a number of novel fillers. Such fillers are useful in both free radically polymerizable compositions, cationically polymerizable compositions, and hybrid compositions featuring both free radically and cationically polymerizable components. Some of these fillers have high clarity and form composites having relatively low opacity with respect to visible light. Some of these fillers also exhibit low surface area and low residual porosity.
One filler is a melt-derived filler that includes 5-25% by weight aluminum oxide, 10-35% by weight boron oxide, 15-50% by weight lanthanum oxide, and 20-50% by weight silicon oxide.
Another filler is a melt-derived filler that includes 10-30% by weight aluminum oxide, 10-40% by weight boron oxide, 20-50% by weight silicon oxide, and 15-40% by weight tantalum oxide.
A third filler is a melt-derived filler that includes 5-30% by weight aluminum oxide, 5-40% by weight boron oxide, 0-15% by weight lanthanum oxide, 25-55% by weight silicon oxide, and 10-40% by weight zinc oxide.
A fourth filler is a melt-derived filler that includes 15-30% by weight aluminum oxide, 15-30% by weight boron oxide, 20-50% by weight silicon oxide, and 15-40% by weight ytterbium oxide.
A fifth filler is in the form of non vitreous microparticles prepared by a sol-gel method in which an aqueous or organic dispersion or sol of amorphous silicon oxide is mixed with an aqueous or organic dispersion, sol, or solution of a radiopacifying metal oxide, or precursor organic or inorganic compound. The microparticles are substantially free of crystalline microregions or inhomogeneities detectable via powder x-ray diffraction. A sixth filler is in the form of non vitreous microparticles prepared by a sol-gel method in which an aqueous or organic dispersion or sol of amorphous silicon oxide is mixed with an aqueous or organic dispersion, sol, or solution of a radiopacifying metal oxide, or precursor organic or inorganic compound. The microparticles include: (i) a plurality of amorphous microregions comprising oxygen and silicon, (ii) a plurality of radiopacifying, semicrystalline, metal oxide microregions, and (iii) no greater than about 40% by weight of B2O3 or P2O5. The amorphous microregions are substantially uniformly interspersed with the semicrystalline microregions. In addition, the microparticles are substantially free of crystalline microregions or inhomogeneities having diameters greater than 0.4 micrometers.
Other features and advantages of the invention will be apparent from the following description of preferred embodiments thereof, and from the claims.